T Cells and Vascular Inflammation

T cells are critical regulatory and effector cells in vascular inflammation. T-cell activation as well as T-cell tolerance is the end result of a complex integration of signals through the T-cell receptor and co-stimulatory molecules as well as signals from regulatory T cells. Naïve CD4 T cells are pluripotent and can differentiate into an increasing number of effector lineages such as Th1, Th2, Th9, Th17 and follicular helper T cells or into regulatory T cells (Treg). Lineage commitment is not irreversible and some plasticity persists in differentiated T cells, in particular Tregs can differentiate into Th17. Disease patterns in vasculitides is influenced by the effector type as well as the stage of T-cell differentiation. Accumulation of end-differentiated T-effector cells is frequently associated with vascular inflammation. Molecular characterization of the signaling events in T-cell activation, T-cell tolerance and T-cell differentiation has been instrumental in identifying targets for developing T-cell-directed therapies. Understanding how T-cell effector functions contribute to different vasculitides provides a framework to decide which and how these treatments should be explored.